Bruxism (tooth grinding when not masticating or swallowing) and tooth clenching (isometric muscle contraction with the teeth in contact) are common functional jaw disturbances.
The isometric contraction produced during clenching is even more tiring to the muscles than the isotonic contraction produced during bruxism. However, bruxing forces are considerable. The volume of the sound produced during grinding is substantial and is difficult to simulate voluntarily. This excitation of the jaw closing muscles appears to serve as a tension-relieving mechanism Some individuals are more susceptible to environmental stress, and respond by increased jaw muscle tension, either at night or with daytime clenching. It has been postulated that the protective mechanism in these individuals has been dulled down. Experimental evidence has shown that in addition to discomfort, damage accompanies such muscular hyperactivity.
Para-functional oral habits, particularly bruxism, and tooth clenching as well as myofacial pain are common components of temporomandibular joint (TMJ) dysfunction. TMJ disorders are estimated to affect from 10 to 30 million Americans with approximately one million new patients diagnosed yearly. The majority of the sufferers are women, ages 20 to 40. It has been demonstrated that tooth clenching or tooth grinding in response to stressful life situations is associated with or may actually induce depression, anxiety, frustration and chronic pain. These symptoms are more marked in patients with TMJ problems than in control subjects. The regular repetitive side-to-side tooth contacts of bruxism differ from the haphazard pattern observed during mastication. Bruxism or clenching at night is often totally beyond the patient's awareness. A classic presentation is pain in front of and just below the tragus, with radiation to the ear, lower jaw, cheek and temple. Pain is usually worse in the morning and may occur in cyclical episodes. In response to questioning, these individuals often describe (1) orofacial or jaw pain and other symptoms on arising, (2) posterior tooth soreness on arising, (3) teeth pressed together on awakening, and (4) jaw “tiredness” during chewing. Typical wear facets and/or worn teeth can be seen in strong bruxers, but not in those who clench. Nocturnal monitoring of masseteric electromyographic (EMG) activity in bruxers showed marked increases of EMG activity (bruxism) during periods of life situational stress. These habits abuse the masticatory muscles, especially the masseter, and result in muscle dysfunction, i.e. muscle spasm and trigger points. Muscle spasm is the commonest manifestation of musculoskeletal pathology, and can be defined as a prolonged continuous contraction of muscle. Trigger points are small., ischemic, tender points in the involved muscle and its associated area caused by abnormal functioning (overloading) of the muscle. The trigger points can refer pain and other symptoms, especially jaw tiredness. Trigger points are undetectable by the usual muscle tests, such as application of maximal resistance to the muscle. Muscles in spasm respond to these tests by demonstrating pain or other symptoms. Due to a lowered skin resistance (impedance) over the point, trigger points can be verified by various electronic detectors. In addition to referring pain, they perpetuate muscle tenderness, and prevent full muscle lengthening (relaxation). In bruxers or clenchers, multiple trigger points are almost always found in the deep vertical fibers of the masseter muscle, just under the temporomandibular joint, and often in the posterior belly of the digastric and stylohyoid muscles, anterior and inferior to the ear lobe(s). Trigger points in these muscles often refer symptoms, such as congestion, pain, and tinnitus to the ears, as well as giving rise to swallowing difficulties, i.e., eustachian tube dysfunction This is often confusing in treatment, since, in these cases, objective signs of ear dysfunction are absent.
Bruxism and/or clenching can be initiated by systemic, psychological, occupational and occlusal factors. Often, a combination of general and local factors influencing each other set up a vicious cycle. Standard treatment for the above parafunctional habits generally consists of one or more of the following; physical therapy and namely prescribed exercises, massage, application of moist heat, or cold in the form of ice packs, behavior modification, medication taken orally including non-steroidal anti-inflammatories, muscle relaxants, tricyclic antidepressants, tranquilizers or anti-anxiety drugs. Behavior modification, with stress reduction as its goal, generally consists of counseling on life style and relaxation therapy and/or biofeedback. Biofeedback uses equipment to measure biologic activity, e.g., surface electromyography to measure muscle activity. A “feed back loop” allows the patient to receive immediate information (feedback). The patient, guided by this information, is then trained to reduce excessive muscular activity by appropriate thought processes (U.S. Pat. Nos. 6,117,092, 6,270,466). Various devices have been produced for preventing bruxism, and they include those which electrically stimulate the jaw (U.S. Pat. No. 4,669,477), the neck (U.S. Pat. No. 4,715,367), the lip (Clark, G. T. et al CDA Journal 21(1):19-30, 1993), the mouth (U.S. Pat. Nos. 4,995,404; 6,490,520), or tooth (U.S. Pat. No. 5,553,626) and those which use mild aversive shocks upon detecting the occurrence of bruxism (U.S. Pat. No. 4,715,367), and those which alarm the user upon detection of bruxism (U.S. Pat. Nos. 4,220,142; 4,976,618; 4,979,516; 4,989,616; 4,995,404; 5,078,153; 5,586,562; 6,164,278). Control of bruxism or clenching by medication usually involves muscle relaxants, such as diazepam (U.S. Pat. No. 6,638,241) or cyclobenzaprine (U.S. Pat. No. 6,632,843). These medications when taken orally are associated with side effects; particularly sedation, and dependency, in the case of diazepam can be a problem. Other prescribed medications resembling muscle relaxants, such as Esgic (butalbital, acetaminophen and caffeine), have generalized depressive effects on the central nervous system and can be addictive. Recently, neurotoxins such as botulinum toxin have been used to treat myofacial pain and bruxism (U.S. Pat. No. 6,333,037). Biosensory devices have also been conceived for the automatic delivery of the medications (U.S. Pat. No. 6,638,241).
Removable dental appliances are commonly prescribed to control or eliminate these harmful oral habits (Rugh, J. D. et al Journal of Craniomandibular Disorders 3(4):203-210, 1989). These appliances, usually designed with flat occlusal surfaces, fit over the maxillary or mandibular teeth to prevent complete closure, since the powerful jaw closing muscles (masseter, temporalis, medial pterygoid) cannot shorten completely, they cannot contract as forcefully. Additionally, the flat occlusal surface eliminates the usual triggers, abrasive contact between irregular tooth surfaces.
Occlusal adjustments, elimination of perceived excessive tooth contact by grinding, may be effective. However if incorrect surfaces are removed, the situation may worsen. Unlike appliances, which can be modified by adding or subtracting plastic, elimination of tooth surface is irreversible.